The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The assignee of the present disclosure is a leader in the field of environmental control system used in small, medium and large scale data centers. As opposed to the more conventional air side economizer, the system described in this application uses a pumped refrigerant economizer. A pumped refrigerant economizer system utilizes a liquid pump to circulate refrigerant instead of operating the compressor when the indoor & outdoor temperature conditions are suitable to provide cooling without requiring a vapor compression cycle.
A pumped refrigerant economizer system also typically uses a system of sensors to measure the outside and inside air conditions, and if the outside conditions are suitable to allow cooling without requiring compression of the refrigerant, a liquid pump is used in place of the compressor to provide refrigerant flow through the system. This mode of operation is known in the industry as the “pump mode”. Running in the pumped mode reduces or eliminates the need for the air conditioning system's compressor(s) to run. This results in a significant energy savings for cooling the space. In “compressor mode” of operation, the compressor(s) of the system is/are running to supply the cooling needs for the space.
When running in pump mode, however, care must be taken to not incur damage to various components of the system. In particular, it is understood that the lack of superheat leaving the evaporator during the pump mode can eventually lead to excessive liquid refrigerant collecting in the crankcase of the compressor. This can have detrimental effects on the compressor if a sufficient quantity of liquid refrigerant has collected in the compressor crankcase during the pump mode, and then the compressor mode is started. Excessive liquid accumulating in the crankcase (i.e., sump) of the compressor may potentially cause various issues such as sump frosting and/or oil foaming, oil dilution and/or washout when the compressor attempts to start up during transitions from the pump mode to the compressor mode.
While present day economizer systems adjust the system's EEV (Electronic Expansion Valve) to maintain appropriate pump differential pressure while operating in the pump mode, there is no control over the superheat leaving the evaporator when the system is running in the pump mode. Accordingly, some means to control and limit the liquid refrigerant build-up in the compressor during the pump mode of operation is needed.